public class DocValuesTermsQuery extends Query
Query that only accepts documents whose
term value in the specified field is contained in the
provided set of allowed terms.
This is the same functionality as TermsQuery (from queries/), but because of drastically different implementations, they also have different performance characteristics, as described below.
NOTE: be very careful using this query: it is
typically much slower than using TermsQuery,
but in certain specialized cases may be faster.
With each search, this query translates the specified
set of Terms into a private LongBitSet keyed by
term number per unique IndexReader (normally one
reader per segment). Then, during matching, the term
number for each docID is retrieved from the cache and
then checked for inclusion using the LongBitSet.
Since all testing is done using RAM resident data
structures, performance should be very fast, most likely
fast enough to not require further caching of the
DocIdSet for each possible combination of terms.
However, because docIDs are simply scanned linearly, an
index with a great many small documents may find this
linear scan too costly.
In contrast, TermsQuery builds up an FixedBitSet,
keyed by docID, every time it's created, by enumerating
through all matching docs using PostingsEnum to seek
and scan through each term's docID list. While there is
no linear scan of all docIDs, besides the allocation of
the underlying array in the FixedBitSet, this
approach requires a number of "disk seeks" in proportion
to the number of terms, which can be exceptionally costly
when there are cache misses in the OS's IO cache.
Generally, this filter will be slower on the first invocation for a given field, but subsequent invocations, even if you change the allowed set of Terms, should be faster than TermsQuery, especially as the number of Terms being matched increases. If you are matching only a very small number of terms, and those terms in turn match a very small number of documents, TermsQuery may perform faster.
Which query is best is very application dependent.
| Constructor and Description |
|---|
DocValuesTermsQuery(String field,
BytesRef... terms) |
DocValuesTermsQuery(String field,
Collection<BytesRef> terms) |
DocValuesTermsQuery(String field,
String... terms) |
| Modifier and Type | Method and Description |
|---|---|
Weight |
createWeight(IndexSearcher searcher,
boolean needsScores) |
boolean |
equals(Object obj) |
int |
hashCode() |
String |
toString(String defaultField) |
public DocValuesTermsQuery(String field, Collection<BytesRef> terms)
public Weight createWeight(IndexSearcher searcher, boolean needsScores) throws IOException
createWeight in class QueryIOExceptionCopyright © 2000-2016 Apache Software Foundation. All Rights Reserved.